Mario Williams hurled that ugly primate off his back last season with a 14-sack explosion. Only two NFL players had more. But as a team, the Texans lagged, again, when it came to making the opposing passer squirm and fret.

Just once in their six seasons — and barely then, when they tied for 14th in 2005 — have the Texans finished in the top half of the NFL in sacks. Even with Williams’ promise-fulfilling outburst in 2007 after a quiet rookie reason, the team ranked 21st because all the other Texans combined to dump the quarterback a scant 17 times. So a priority coming into training camp this summer was making a quantum leap in pass-rush quality, especially from the front four.

Halfway through an otherwise encouraging preseason, it’s not happening. But is it too early to worry?

“It’s never too early to worry,” defensive coordinator Richard Smith said. “We’ve got to get better.”

Improvement was supposed to come in part from the addition of free agent Rosevelt Colvin, a 10-year veteran with a knack for giving passers happy feet. Unfortunately, the aftereffects of a foot injury that ended his 2007 season with New England after 11 games, in combination with his having to learning a new system, new teammates and a new position — the 250-pounder is lining up at end instead of blitzing as a linebacker — has him performing at a subpar level .

“I’m trying to knock a little rust off,” Colvin said. “I feel like it’s coming. But I need to get it down sooner rather than later.”

He played so-so against Denver. The coaches say he showed more against New Orleans, although the evidence wasn’t overt. The Saints’ Drew Brees was rarely stressed Saturday. Broncos quarterbacks were similarly unthreatened. The Texans have just one sack in eight quarters, by end Tim Bulman.

Even Williams has been quiet. But after his giant strides last fall, nobody is panicking.

“It’s always about the pass rush,” Colvin said. “You get to the quarterback, you disrupt the offense. It’s that simple. It’s the preseason, but this is when we set the foundation for the regular season. Right now we’d like to put more pressure on the quarterback, and we’re continually in the process of trying to do that. It’s the coaches’ job to put players in position to make plays. They’re in the process of finding that right mix.”

Despite his experience — four seasons with the Chicago Bears, five with New England — Colvin feels a lot like a rookie.

“I’m really trying to focus on getting the basic techniques down,” he said. “It’s always different when you come to a new team. It’s basically old stuff, but you have to place yourself in a new spot. Every day they bring in something new. Hopefully I can find my niche, get to the point where I contribute more and be the person they’re looking for. I’d like to make a home for myself here.

“I would not say I’m fully comfortable. It’s been 10 years since I played full-time defensive end. It’s a lot different on your body, with different reads and being covered up sometimes. You’re not always on the edge.”

Every chance

Colvin, 30, will be given every opportunity to prove himself against Dallas on Friday night and Tampa Bay next week. The Texans didn’t sign him on a wing and a prayer. They were counting on him to make a difference.

“We’ve got two weeks to see how much progress he can make,” Smith said. “We’re hoping like heck he can get where he needs to be. As you fully well know, we need to improve our pressure on the quarterback, and I don’t mean by blitzing or dogging people. We want good four-man pressure. ”

Leadership qualities

Being well-spoken and possessing all the leadership qualities coaches seek out, Colvin brings the same things to the Texans’ table that N.D. Kalu does, and he’s two years younger. But feeling threatened by Colvin’s presence, Kalu is having an excellent preseason. The problem: Can the Texans afford to tie up two roster spots on aging, undersized defensive ends, however good for locker room chemistry they might be?

“I know that he’s capable of rushing the passer — I’ve played against him too many times,” coach Gary Kubiak said of Colvin. “I didn’t see bringing him in to be a gamble. I thought he could help us, and I still hope he can.

“Honestly, we haven’t been very good with four guys getting to the quarterback. But we’re going to keep working on it. We have to. We proved to ourselves last year that if we’ve got to call pressure (blitzes) all the time to get to the quarterback, our team is probably in trouble.”